(CNN) - One is a former hospital. Another is a retrofitted superstore. One is a tent city with the capacity to grow.
These are the places where most infants and children are held after they're separated from their families, who crossed the US-Mexico border without prior authorization.
Children are sent to different facilities across the country depending on their age, gender, history of behavioral issues or criminal activity, or medical needs. These centers are overseen by the Department of Health and Human Services' Office of Refugee Resettlement, which said the average stay is 56 days.
Some are newly built "tender age" facilities to accommodate the influx of children under 13 who have been separated from their parents under the Trump administration's zero-tolerance immigration enforcement policy. One of those facilities is a former private home about 20 miles from the US-Mexico border in Texas town of Combes, operated by Southwest Key Programs.
A set of black strollers and a small playground were the only visible signs of the roughly 60 children -- ranging in age from infants to 10 years old -- housed inside.
A "tender age" facility in Harlingen, Texas, run by Southwest Key, has a soccer goal and small playground in its yard.
At another "tender age" facility, called BCFS, in Raymondville, Texas, a volleyball net and a pool are visible on the grounds.
Others facilities have existed for years as shelters for unaccompanied migrant children who enter the US alone or were separated from their families.
But the administration has been tight-lipped over who's going where, exactly.
The Homestead Temporary Shelter for Unaccompanied Children in Florida is a former Job Corps site that has been used as a shelter for unaccompanied minors since 2014.
Photos taken this week showed boys and girls at the shelter. On Tuesday, Florida Gov. Rick Scott sent a letter to Health and Human Services Secretary Alex Azar expressing concern over "unconfirmed reports" that the shelter is "potentially holding children who have been forcibly removed from their families."
In his letter, Scott demanded confirmation of reports that children separated from their families were being sent to the Homestead shelter. He also requested information about health screening protocols at the border and what, if any, health and education resources were being provided to children placed in Florida.
Another center is about 30 miles from the nation's capital in Bristow, Virginia. Youth for Tomorrow, a non profit founded by former Washington Redskins Coach Joe Gibbs, has been partially used as a shelter for unaccompanied minors for several years.
Photos released this week by HHS showed girls wearing uniforms sitting in an auditorium, a set of baby high chairs, a room with cribs and a woman carrying a baby.
In Texas, the administration opened a new temporary shelter in June on federal land in Tornillo to accommodate the influx of children.
The shelter consists of what an HHS spokesman called "soft-sided structures" resembling tents equipped with air-conditioning to withstand the high temperatures
The Tornillo camp was originally built with 360 beds and room for expansion.
At the Central Processing Center in McAllen, US Border Patrol agents conduct intake of migrants.
After intake, people are taken into custody while they await prosecution or deportation proceedings.
Images of people held in cages have drawn widespread criticism and calls for reform of immigration enforcement policies.
Democratic Texas Rep. Filemon Vela Jr. toured a new shelter in Brownsville for children under 13, pictured below. The center is managed by the nonprofit Southwest Key Programs in coordination with the Health and Human Services' Office of Refugee Resettlement.
He said the former hospital has about 80 children under the age of 10 -- 40 of whom he believed were separated from their parents as a result of the zero-tolerance policy. One room held four infants, two of whom were accompanied by their teenaged mothers, he said. The children receive constant attention, he said. "People are doing what they can under the circumstances."
Elsewhere in Brownsville, Southwest Key Programs operates the Casa Padre Shelter inside the 250,000-square-foot shell of a former Walmart superstore.
The shelter, which houses boys ages 10 to 17, has seen its numbers surge since it opened last year. The rooms have no doors or ceilings, and five cot-like beds have been squeezed into bedrooms built originally for four. Currently, it houses 1,469 people.
Southwest Key CEO Juan Sanchez said his organization runs childcare facilities, not detention centers.
"Our job is to take care of kids and that's what we do and we do it very well," he told CNN affiliate KTRK. "Regardless of policy and whatever's going on politically, that's not our job. Our job is to take care of kids."
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